Intravascular ultrasound (IVUS) imaging is a technology that enables realtime tomographic assessment of the arterial wall and it is increasingly employed to assist in selecting and evaluating therapeutic interventions. While new catheter designs have been developed, the current technology for ultrasound transducer array fabrication and electronics integration has limited the improvement of image quality and further development of advanced techniques for in vivo detection of the progression of atherosclerotic disease. Over the past two years, with NIH funding, we focused on improving Capacitive Micromachined Ultrasonic Transducer (CMUT) technology for IVUS, and removed significant barriers for implementation of high performance arrays: We developed novel dual-electrode CMUTs with efficiency and bandwidth rivaling single crystal piezoelectric transducer array elements, and more importantly, we demonstrated monolithic integration of front-end imaging electronics and CMUT arrays on the same silicon chip. We also performed initial imaging studies on medically relevant samples with CMUT-IVUS arrays operating in the 20-50MHz range and established infrastructure and collaborations for implementation of a prototype CMUT-IVUS catheter. Based on these advances, in this competitive renewal application we seek to demonstrate the feasibility of IVUS catheters using high performance CMUTs with integrated electronics for clinical settings, and further develop CMUT designs and arrays for challenging IVUS applications. We will develop high performance mass loaded dual-electrode annular CMUT phased arrays for IVUS with monolithic integrated electronics operating in the 30-50MHz range to provide the high resolution and penetration depth required for vasa-vasorum imaging and the bandwidth and resolution for improved composition imaging. We propose to implement a prototype side looking CMUT-IVUS catheter with annular arrays, and use it on relevant imaging phantoms for validation. This study will facilitate translation of research on revolutionary, lead free CMUT technology into clinical studies for detection and management of coronary and peripheral arterial diseases. This study will also serve as a paradigm for a broad range of ultrasound imaging applications that would benefit from advanced transducer technology with integrated electronics.